Filters formed from coaxial cavity resonators are widely used in data transmission systems and, in particular, telecommunications systems. In particular, filters formed from cavity resonators are often used in base stations, radar systems, amplifier linearization systems, point-to-point radio and radio frequency (RF) signal cancellation systems.
Although filters tend to be chosen or designed depending on a particular application, there are often certain desirable characteristics common to all filter realisations. For example, the amount of insertion loss in the pass band of a filter ought to be as low as possible, whilst the attenuation in the stop band should be as high as possible. Furthermore, in some applications the frequency separation between the pass band and stop band (i.e., guard band) may need to be very small, which can require filters of high order to be deployed in order to achieve such a specific requirement. However, requirements for high order filters are typically followed by an increase in cost due to a greater number of components and an increase in the need for space which is often at a premium in telecommunications implementations such as those listed above.
One challenging task in filter design is that of reducing the size of the filters whilst retaining their operational characteristics, including electrical performance. It is desired to provide smaller filters which have performance characteristics that are comparable to much larger structures. With the arrival of small cells within telecommunication systems and the need to provide multiband solutions within a similar footprint to that of single band solutions, there is an increasing need to reduce the size of various telecommunication components including filters.
It is desired to provide a cavity assembly which can be used in a filter to address some of the issues currently being faced in filter design.